US2252580A - Electron discharge device - Google Patents

Description

Aug. 12, 1941'. H. ROTHE ET AL ELECTRON DISCHARGE DEVICE F'i'led March 23, 1939 I NV EN TORS HORST ROTHE AND WERNER KLEEN I a/%q ATTORNEY.

Patented Aug. 12, 1941 UNITE 2,252,580 ELECTRON nrsommon DEVICE Horst Rothe and Werner Kleen, Berlin, Germany, assignors to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of. Germany Application March 23, 1939, Serial No. 263,604 In Germany April 8, 1938 Claims.

The present invention relates to electron discharge tubes for superheterodyne reception and utilizing double control of a discharge current flowing from a cathode to an anode, the first control action being by a control grid interposed between cathode and a screen electrode and to control electrode to which for example a local oscillator voltage may be applied. A modulated intermediate frequency alternating voltage and current are produced in the output of the tube.

It has been found that under certain circumstances when a tube of the type described is used as a so-called mixer tube, transit time effects cause grid current to flow in the first or signal grid when the second or oscillator grid voltage is operating at high frequency. This effect is due to electrons which are periodically repelled by the oscillator or second grid when it swings negative, that is electrons which are in the space between the signal grid and oscillator grid when the oscillator swings negative are returned to the signal grid. Most of the so-called transit time loading found in tubes of this type is due to the electrons repelled by the oscillator grid to the vicinity of the first grid.

A tube of the kind under consideration has been proposed in which the first control grid surrounding the cathode is followed by a screen electrode which is permeable to electrons only within a restricted portion of its circumference, While the second control electrode next following has rod-shaped elements. positioned in front of the current-permeable parts of the preceding screen electrode. Electrons travelling from the cathode to the anode are deflected from a straight radial path to the anode toward the impermeable portions of the first screen grid so that when these electrons are returned they strike the impermeable portions and are absorbed by the screen grid. In this way the repelled electrons are removed from the space without returning to the signal grid.

It is the principal object of our invention to provide an improved type of electron discharge device of the so-called mixer type for use in superheterodyne receivers, more particularly to provide such a tube in which the electron transit time elfects described are substantially eliminated.

The novel features which we believe to be char-, acteristic of our invention are set forth with particularity in the appended claims, but the invention itself will best-be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a transverse section of a tube of the type described and previously proposed for correcting transit time defects, Figures 2 and 3 are transverse sections of electron discharge devices made according to our invention.

In Figure 1 showing the type of tube previously proposed the electron system comprises the thermionic cathode I designed either for indirect or direct heating and the first control grid 2. The latter is preferably of oval cross-sectional form, and it is supported by two supporting members or side rods 3 secured at the ends of, maximum diameter of the grid. This shape is chosen for the grid because it insures a certain amount of focusing of the electronic current in that the current is crowded together and concentrated in the direction of the smallest diameter. Next comes the first screen electrode 4 which consists, for instance, of two halves 5 impermeable to electrons and current flow and so disposed that passages or openings are provided between them for the discharge current. The parts impermeable to current consist, for example, of sheet material or of a very densely woven wire gauze or reticulate structure. The openings for the passage of current are suitably covered by grid wires 6 to enhance the screening effect. The cross-section of the screen electrode 4 is suitably chosen also oval in order to increase the focusing effect brought to act upon the discharge current. For reasons that shall be set forth more fully further below, extensions or funnel-shaped expansions or hopper portions 1 are provided at the edges of the current-permeable parts 6. Following the screen electrodes 4 is the second control electrode 8 the most essential parts of which consist of the grid supports or side rods 9 which are mounted opposite the current-permeable parts 6 of the screen electrode 4. These same rods or supporting means 9 could serve at the same time to support the second control electrode, although also accessory supporting members Ill could be provided being mounted in the same plane as the rods 3 of the first control grid 2. Under certain circumstances, the second control electrode could consist of nothing else but the rods or upright supports 9; and these latter, if desired, could be also in the form of sheet-metal strips in radial position relative to the cathode or filament. The plate or anode l I either could surround the inner electrodes all around or else it could be limited to those parts of the periphery which are likely to be reached by electrons. Between the second control electrode and the anode or plate is preferably interposed a second screen electrode I2. It will be understood that naturally additional accessory electrodes such as a suppressor or cathode grid could be mounted between the screen grid [2 and the plate ll. However, to carry the present invention into practice, five electrodes will suffice, that is to say, cathode, first control electrode, screen electrode, second control electrode and plate. An envelope l5 encloses the electrodes.

If the tube described is to be used as a mixer tube, then the incoming (signal) oscillations are fed to the first grid 2, whereas the second control electrode 8 or the supporting members or stays 9 are impressed with the heterodyne (local) oscillation. This kind of circuit organization is expedient for the reason that, as will be remembered, it is just the input circuit that is to be safeguarded against additional damping occasioned by returning electrons. The screen electrode 4, in line with general practice, is impressed with a fixed positive biasing potential. The output potentials are delivered at the plate or anode. The heterodyne or local oscillation could be generated also in the same tube by disposing, for instance, a positively biased auxiliary electrode directly in front or in the rear of the second control electrode 8, the circuit containing this positively biased auxiliary electrode being in regenerative relationship with the circuit of the second control electrode thus resulting in the generation of the local oscillation.

In order to fully understand the operation of the electrode system and its merits it is necessary to examine the paths or trajectories of the electrons. The electron path [3 holds good for such a high effective potential of the second control electrode 8 that electrons will be passed to the anode or plate I I. But if the effective potential of the second control electrode 8 becomes lower, then the electron paths follow roughly curve [4, that is to say, they are no longer able to traverse the second control electrode, but they reverse their direction of flight. What is then of essential importance is the presence of the rods or supports 9 the effects of which, indeed,

is that the electrons even on their outgoing trip are deflected laterally. If, then, the electrons are reflected from. an equipotential surface anteriorly of the second control electrode which proves impermeable for them (and for these electrons there applies the law that the angle of incidence is equal to the angle of reflection in reference to the perpendicular line to the reflecting surface), they do not travel back along the same route, but rather extend their trajectories in a lateral direction with the result that they no longer strike the permeable parts 6 of the first screen electrode 4, but rather impinge upon the unbroken and solid portions 5. In other words, the rearward flow to the first control grid 2 is avoided. In this entire action, also the hopper or funnel-shaped portions I mounted on the edges of the first screen electrode play a certain part in that they prevent such electrons as just happen to skirt the edges from entering in spite of all the space confined by the first screen electrode. This protective action is produced by virtue of the fact that the extension pieces. I being directed roughly radially to the cathode, result in a tangential field component so that such electrons as would otherwise hit permeable portions of the screen electrode are attracted by them.

The flaring extensions I perform another role of importance. Inasmuch as they project into the space between the positive screen electrode 4 and the second control electrode 8, the potential in this space is more positive than it would be in the absence of the extension pieces. And this means an accelerated motion of the electrons and thus a briefer transit time of the electrons, a feature which is particularly important in connection with operation at ultra-short waves.

The invention is illustrated in Figure 2. The underlying idea here is to make the effective potential along the second tubular or cylindrical control grid 8 so different that the deflecting effect of the grid rods or supports 9 is assisted and the electrons are pulled laterally. This is insured by making the distance between the second control grid and the positively biased second screen electrode next following unequal. In this way in the neighborhood of the control electrode supports the effective potential of the control grid is greater than laterally thereto. The grid pull of the second screen grid across the second control grid, therefore, will be less in the vicinity of the rods or upright supports than laterally thereto. The result is that the second screen grid in the neighborhood of the controlgrid rods contributes less in a positive way to the effective potential'of the second control grid. In other words the space potential between the first screen grid electrode and second control grid 8 on either side of the rods 9 is more positive than the space potential between the rods and the permeable portions of the screen grid through which radial electron beams emerge. Hence, the electrons will experience a deflection towards the positive lateral portions of the second control grid. In Figure 2 the same reference numerals are used as in Figure 1. A distinction regarding the construction exists only as regards the shape of the second screen grid [2. This grid is of rhombic cross-sectional form with the result that the distance a of the screen-grid surface IZ from the control grid rods 9 measured in radial direction is considerably greater than the distance D laterally thereto removed 45. The effective potential in the control-grid surface therefore is more positive in the neighborhood of b than in the vicinity of the rods 9. The electrons coming from the cathode, therefore, after their exit from the first screen electrode 4, on the one hand, are forced laterally by action of the control grid rods, while, on the other hand, they are pulled sideways by the more positive portions of the control-grid surface, with the consequence that they will so much more safely reach the solid portions of the first screen electrode, if they are unable to travel all the way to the anode or plate. The rhombic crosssectional form, of course, is merely chosen here by way of example. The second screen grid, as a matter of fact, could consist also of curvilinear surface portions provided that the rules before laid down regarding the change in distance in reference to the second control grid are observed.

In the modification in Figure 3 the field causing lateral deflection of the electrons is set up by choosing unequal distances between the second control grid 8 and the inner screen electrode by making it at the place marked 0 greater in refernce to the rods 9 than at the points marked d" located laterally thereto. The so-called reverse grid transparency brought about. b the first screen electrode upon the second control grid, therefore, is greater at the points markedd than at e, and the result is the production at the firstnamed place of a more positive potential upon the second control grid which causes a lateral pull to act upon the electrons, The second screen grid l2 could simply be made of an oval cross section. While it is true that the distance from different portions of the second control grid is different, this fact will be more or less balanced and compensated so far as the second control grid is concerned by the rods 9 which shield the action of the second screen-grid potential. The consequence is the pull of the second screen grid at this point where the rods are will not be any greater than on the sides, where, it is not screened, but where it is spaced a greater distance apart from the control-grid surface.

As regards the construction and mounting of the electrode system and assembly it will have to be noted that, inside the scope and spirit of the invention, there are conceivable a great many modifications. For instance, parts of the other electrodes located posteriorly of the solid portions of the first screen electrode, in so far as they are not located inside the, electron stream, could simply be omitted as indicated, in fact, in the case of the exemplified embodiments comprising a two-part anode consisting of parts I I. What is thus realized is a reduction of the capacitance active between the electrodes. On the other hand, it would also be possible to close or complete the periphery of the plate or anode, and this may under certain circumstances simplify its manufacture and supporting and insure a screening of the inner electrodes against external stray fields. It is, moreover, not necessary to work with two electron beams as shown in the exemplified embodiments, in fact, either a greater number of electron beams or merely one such beam could be used.

The object of the invention affords a chance, also for wavelengths less than 10 meters, to have recourse to the so-called multiplicative mixing, while heretofore it has been feasible only to resort to additive mixing because of the heavy current caused to flow to the first control grid as a result of transitime phenomena, in which both input (signal) and heterodyne or local oscillation potential were both impressed upon one and the same grid. However, the utility of the tube is not restricted to the ultra-short wave range, particularly because of the fact that more modern broadcast receiver tubes are required to operate just as well with longer as with shorter waves. The same rule applies particularly also to receivers which in the future will be equipped with a short-wave part and, after inception of television, with an ultra-short-wave part.

The tube here disclosed, moreover, could be used in addition to mixing also for other purposes such as modulation. It is also feasible to create a push-pull arrangement in that the second control grid and optionally also the anode consist each of two halves that are not interconnected. For instance, modulation circuit organizations working with suppressed carrier wave could be equipped with tubes of the said sort.

While we have indicated the preferred embodiments of our invention of which we are now aware and have also indicated only one specific ployed, it will be apparent that our invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which itis employed without departing from the scope of our invention as set forth in the appended claims.

What we claim as new is:

. 1.. An electron discharge device having a cathodev for supplying electrons and an anode for receiving said electrons, a grid surrounding said cathode, a screen grid surrounding said control grid and cathode and provided with portions impermeable to electrons and other portions permeable to-electrons for providing radial electron beams from said cathode, a second control grid surrounding said screen grid and having rods positioned in the path of the electron beams and a second screen grid surrounding said second control grid, portions of said second screen grid and second control grid being more closely spaced at the impermeable portions of the first screen grid than other portions for providing, during operation of the tube, a, more positive space potential between said first screen grid and said second control grid at the impermeable portions of the first screen grid than the space potential between the permeable portions of the first screen grid and the rods of said second control grid.

2. An electron discharge device having a cathode surrounded by a control grid, a screen grid surrounding said control grid and having portions impermeable to electrons and other portions permeable to electrons whereby beams of electrons from said cathode are formed, a tubular second control grid surrounding said screen grid and provided with side rods in the path of said electron beams, a second screen grid surrounding said second control grid and an anode, said second screen grid being of rectangular cross section and spaced more closely adjacent the second control grid opposite the impermeable portions of the first screen grid than opposite the portions of the control grid at which said side rods are positioned within the electron beams.

3. An electron discharge device having a cathode surrounded by a control grid and screen grid having portions impermeable to electrons and other portions permeable to electrons for providing electron beams from said cathode, a control grid of rectangular cross section surrounding said screen grid and provided with side rods positioned in the path of the electron beams, said side rods being positioned at the corners of the rectangular cross section of said grid, the space between said screen grid and said second control grid being less at the portions opposite the impermeable portions of the screen grid and greater at points where said side rods are positioned, a second screen grid surrounding said control grid and an anode for receiving electrons from said cathode.

4. An electron discharge device having a cathode surrounded by a control grid and a screen electrode surrounding said control grid and consisting of solid sections impermeable to electrons, said solid sections being spaced apart to provide permeable portions for said electrons whereby beams of electrons are formed from said cathode, a second control grid provided with side rods and surrounding said screen grid and a second screen grid surrounding said second control grid, and an anode for receiving electrons from said cathode, one of the side rods of said second control application for which our invention maybeemgrid being in each of the paths of the electron beams, said second control grid and said'second screen grid having portionsmore closely spaced on opposite sides of the location of the side rods of said second control grid than other portions and between the solid sections of the screen electrode and the second control grid.

5. An electron discharge device having a cathode surrounded by a control grid, a-screen' grid having portions impermeable to electrons and other portions permeable to electrons surrounding said control grid to provide radial electron beams, a second control grid surrounding said screen grid and a second screen grid and an anode, said second control grid having side rods positioned in the path of'the electron beams, said second control grid and said second screen grid having the spacing between said second control grid and said second screen grid less at those portions on opposite sides of the side rods than other portions.

HORST ROTHE.

WERNER KLEEN.

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